1. Field of the Invention
The present invention relates to a radar apparatus, and a holding structure of the radar apparatus.
2. Description of Related Art
As described, for example, in Japanese Patent Application Laid-open No. 2003-240838, it is known to mount a radar apparatus on the inner surface of a bumper of a vehicle so as to be covered by the bumper as a cover member.
However, when a radar apparatus is mounted on the inner surface of a bumper, there is possibility that the radar apparatus is damaged by the bumper when the bumper vibrates even slightly, or when the bumper is hit by a stone or the like.
It may occur that the radar apparatus is mounted not on the inner surface of the bumper, but fixed to a certain member located inside a vehicle body so that there is some distance between the radar apparatus and the bumper. However, in this case, the radar apparatus undergoes significantly large effect of the radar wave reflected from the bumper. That is, in this case, since the input level of the radar wave reflected from the bumper becomes very large with respect to a sensitivity of a receiver of the radar apparatus, and accordingly the level of the received radar wave becomes saturated in a receiver circuit of the receiver, it becomes very difficult for the radar apparatus to accurately detect an obstacle (a detection target), if the radar apparatus is configured to receive the reflected radar wave while transmitting the radar wave.
This is further explained below with reference to FIGS. 8 and 9. FIG. 8 is a diagram explaining an obstacle detecting process performed by the radar apparatus in a normal state, and FIG. 9 is a diagram explaining an obstacle detecting process performed by the radar apparatus when the level of the received radar wave saturates in the receiver circuit.
A receiving antenna of the radar apparatus receives a mixture of the radar wave reflected from the obstacle, and the radar wave reflected from the bumper. This received mixture is converted into digital values by an A/D converter (see (a) and (b) of FIG. 8). By detecting through FFT analysis a peak of the digital values, which corresponds to the obstacle, the obstacle can be detected normally (see (c) of FIG. 8).
That is, in the normal state in which the level of the received reflected radar wave does not exceed the sensitivity range of the receiver circuit, the obstacle can be detected normally. On the other hand, if the level of the received wave saturates in the receiver circuit, that is, if the level of the received reflected radar wave exceeds the sensitivity range of the receiver circuit, portions of the received reflected radar wave outside the sensitivity range are cut off. In this case, a noise level (a noise floor) relative to the input level of the radar wave reflected from the obstacle may rise to such an extent that the radar wave reflected from the obstacle is buried in the noise even after performing FFT, as a result of which it becomes difficult to detect the obstacle (see (b) of FIG. 9).